Separation and purification of alcohols by extractive distillation



APF!l 21, 1953 c. s. cARLsoN ET AL 2,535,992

SEPARATION AND PURIFICATION OF LO'IOLS BY EXTRACTIVE DISTILLATION Filed March 1 49x84? mu, OQ

Patented Apr. 21, 1953 SEPARATIONAND PUR-IFICATION OFALCO- HOLS BY EXTRACTIVE DISTILLATION Carl S. Carlson, Elizabeth, and-Paul V. Smith, Jr.,

Westfield, N. J., assignors-to StandardOil Development Company, a` corporationof Delaware Application March 1, 1949, Serial No. 79,018

(Cl. 2oz- 395) V3 Claims. l

This invention relates uto a method of separating pure alcohol products from crude aqueous 'mixtures of the "alcohols .contaminated by' other typesfof 'oxygenated organic compounds.

Even in very fclose-cut -`fractions `from aqueous products of hydrocarbonsynthesis, carbonyl hydrogenation, hydrocarbon oxidation, or `hydration processes, it is diiiicult to avoid having two or more alcohols present with various other types of `close-boiling organic compounds, such as keton'es `aldehydes. racetals, esters, `'ethers and hydrocarbons. Oneor more of the alcohol componentscan be `separated `frorn'such crude mixtures in a fractional distillation column by ernploying a 'sufficiently large quantity of water as 'a refluxing medium throughout the fractional distillation zone in the column. This type oi operation is suitable for isolating an alcohol which is a major component of the crude mixture, the thus isolated alcohol being retainedin the dilute aqueous bottoms of the raction'ating column; however it has been found desirable to improve on this operation in order to obtain a `further `satisfactory isolation of components from the overhead distillate `of the fractionating column.

the base of the column isa dilute aqueous solution of .the isolatedalcohol.

The vcimeentration vor" water employed in the aqueous internalreiiux depends Vupon the `alcohol components being'separated from the 4mixture but in `any 4event is above 65 mol. percent. iFo'r lexampl'e, when ethanol and -isopropanol :are the alcohol components of the ltotal mixture being separated any concentration 'of `water from 651mol` per cent to `99 mol percentis highly effective. However, when ethanol and `normalipropa'nol are thealcohol` components-of thetotal mixture concentration of water -between`90 and `99 mol percent preferably `about 95 `mol-percent must be employed. The desired water concentration for any particular separationmaybe-de- In accordance with the present invention termined from the relative volatilitiesset forth in Table Ibelow.`

lt is advantageous to remove as-muchiof `the water as possible-from the Arst column distillate andto returnthefthusremoved water to the upper partof theuir-st column as a reiiux. The high watercontent of this reflux-supplements the water-feed to the upper-part oi this lrst column. YIii-some instances, it is possible to -obtain a'tvvoliquid `phase separation ofthe distillate When a sufficient quantity of distillate components have a 10W water-solubility in the cooled distillate.

In order to-maintain a homogeneous liquid on the -plates of thesecond column it is preferred L to keep the waterkcontent of the feed thereto betillation is subjected subsequently to a second y water is supplied mainly at the top of the rectin iication zone of the icolurnn. By having a suiicient water concentration in the internal reflux, the volatilities of the lneutral organic contaminants, and of one or more of the alcohol com- `ponents, are `increased relative `to the volatility pi one of the alcohol componentsto be isolated. Tlieaque'ous Vvapor "inixtur'e y of *the contaminants 'and-of alcohol rendered more volatile -is removed 4overhead 4cfrorn' theffdistllation"column. The vrresi-dualportioulof'the...liquid reiiux'whichreaches low about 1-7 to 20 weight percent. If the iirst column distillate therefore is too highly aqueous it-is recommended that it be concentrated to'a water content of the above iigure. The distillate from the first extractive distillation` zone, or

the organic phase of said distillate inthe event of `phase Separation, is then passed into the second iractionating column wherein the required high concentration of .a1 non-polar solvent is maintained in the internal rei'lux so that in the second fractionating columnthe desired separation of another alcohol from the neutral organic contaminants is accomplished. The non-polar reiiuxing medium used inthe second fractionatin'g column is'inaintained atahighvolume concentration level, e. g., volume 'percent 'to 99 volume percent, preferably "about "-90 volume perceriuin orderto assu're the des'iredseparation 'of lthe non-alcohol vconta-minants in a practical size iractionating column.

lA variety foi mechanical `arrangements may be used for conducting the process and asu-itable sinipliiiedv arrangement is 1shown 'diagram-matieallyinthezaccompanyingdrawing. i

4VIn the `drawimg; l represents Vthe "fi-rst -fractionating column which receives a continuous feed stream of crude alcohol mixtures from inlet line 2 intermediate a rectifying section 3 and a lower stripping section 4, each of these sections being provided with means for obtaining eiicient countercurrent liquid-phase contacting, e. g., such conventional means as bubble plates or packing. A feed stream of a large portion of the water which is to make up the internal refluxing medium that iiows down through column I enters column I from line 5 at the upper part of the rectifying section 3. l

A secondary rectifying section 6 is provided in column I above the primary rectifying section 3 to afford further fractionation which tends'to make the vapors passing upwardly therethrough appr-cach compositions `containing azeotropic proportions of water with the volatilized organic components.

The final rectied vapors are withdrawn overhead from column I through line 1 by which they are passed through a cooling condenser 8 and line I to a liquid receiver 9, wherein the distillate depending upon its composition may or may not separate into two liquid phases, a lower aqueous phase and an upper organic phase. For example when handling ethanol-isopropanol mixtures the overhead distillate in most cases will be one p-hase. When handling a n-propanol or n-butanol cut containing other close boiling oxygenated compounds the overhead from the rst fractionation zone will usually separate into two phases.

A controlled portion of the total distillate or of the lower aqueous phase layer in the event of phase separation in receiver 9 is passed by line I I as external reflux to the upper part of column I. Any excess portion of the separated aqueous phase may be withdrawn from the system by line I2.

In those cases where phase separation is not contemplated or desired the overhead from column I may be conducted directly to column I4 as a vaporous feed without condensation in condenser 8. This is especially feasible in those fractionations in which it has been found (not the subject of this invention) that the separation is more complete in the absence of liquid external reflux to column I.

The bulk of the condensed distillate or of the upper organic phase layer in the event of phase separation is withdrawn from the receiver 9 by line I3 to be transferred to the second fractionating column I4 for fractional distillation in the presence of a high concentration of a non-polar internal reiiuxing medium such as a hydrocarbon oil as will be later described.

The residual portion of the high water content internal refluxing medium which ows through the stripping section 4 to the bottom of column I is a dilute aqueous solution of at least one of the alcohols to be isolated from the initial feed. A portion of this aqueous bottoms from column I is heated, partly Vaporized and recycled by lines I and I6 through a heat exchanger 56, which may supply heat directly or indirectly by a heating medium such as live steam.

Another portion of the aqueous bottoms in column I withdrawn by line I5 is passed by line I6 into an alcohol concentrating column I1, which is equipped in a conventional manner as a fractional distillation column with liquid-vapor contacting means for obtaining rectication of the dilute aqueous alcohol. The concentrated' alcohol vapors may be withdrawn overhead from column I 1 by line I8 through a condenser I 9-'to a'r'eceiver CTI 20. A portion of the distillate from receiver 20 may be returned to the top of column I1 as external reflux by line 2I. Water bottoms are withdrawn from the base of column I1 by line 22. A portion of these water bottoms may be recycled by lines 23 and 24 to the base of column I1 for reboiling in passing'through the reboiler 25. Another portion of the water bottoms from column I1 is passed by line 2B through a heat exchanger 21 for temperature control and then is passed through the feed inlet line 5 to the upper part of column I for supplying water required in the internal reiiux medium that flows down through column I. Any excess of the water bottoms from column I1 are Withdrawn from the system through line 28.

In the event that the dilute aqueous alcohol bottoms from column I contains more than one alcohol component, column I1 may be provided with a side stripper 29 which receives a side stream from one of the rectifying plates in column I1 by line 3d, returns stripped vapors back to column I1 by line 3l and discharges a concentrated alcohol product through line 32. This procedure may be followed for example in the concentration of aqueous ethanol which contains some normal propanol.

The second main fractionating column I4 is equipped like the first main column I with a prmary rectifying section 34, a secondary rectifying zone 59, and a stripping section 35. The condensate from receiver 9 enters column I4 at a point between the rectifying and stripping sections. The solvent feed inlet 36 supplies the solvent which is to constitute the major proportion of the internal liquid reiiuxing medium which ows down through column I4. Vapors from the feed material entering column I4 by line I3 pass upwardly countercurrent to the internal reflux medium and the resulting rectified vapors comprising the second desired product plus Water are withdrawn overhead from column I4 by line 31 which leads the vapors through a cooling condenser 33 to a receiver 39. A portion of the distillate is returned from receiver 39 by line 51 as external reflux to the upper part of column I4 while another portion of the distillate is withdrawn by line 4I from 39 as another concentrated product.V

The presence of secondary rectification zone 59 in column I4 is important in that it is essential that the overhead distillate collected in receiver 39 be free of non-polar solvent. This eliminates the need for an additional solvent recovery step.

The residual internal reiluxing medium which descends through the stripping section 35 in column I4 is withdrawn as bottoms by line 4i) in a substantially anhydrous condition. A portion of this solvent bottoms is reheated and vaporized in heat exchanger 42 for return to base of column I4 by line 43. YThe heating in the heat exchanger 42 may be accomplished by indirect heat exchange with live steam or by other conventional high temperature heat sources. A remaining portion of the solvent bottoms Withdrawn from column I4 by line 4t is passed through line 44 to a stripping column 45 which is utilized for stripping volatile neutral oxygenated compounds from the solvent medium. Column 45 may be a conventional fractionating column with the usual liquid-vapor phase contacting means. tilized neutral oxygenated compounds areY distilled'overhead from column 45 throughline 46' The vola-f message?.

and are passed through cooling.-` condenser 41E' to a` receiver.A 4'8. A 'portion ofthe. distillate is re turnedJ by: line 119i as. externalireuxz to the upper part ,ot column 45- from-receiver t8 and.v a` remaining:y portion of` this distillate is withdrawn asa.

product by line'z,

Stripped;` solvent bottomsare Withdrawn from the baserof thestripping: column. dfbyline 58o' partly; tofbe recycledrby "lines` 5i and' 52 through a reboiler: 53: fr.remainingiportionzoffthe, solventA bottoms from; stripping." column.` tv is passed` by. line- 54- through.. a :heat exchange temperature controller.` 55x for: return` through f `line 3.5: .to the upper. part; of:` column Moinr ordertorsupplywtheV high; solvent` concentration.; required; inthe inter-` nal.; liquid.:` reiiuxing: medium; that.` vflows.: down:`

through columna-.1.41.` Anyrfdesreda portion ofthe..

drawn.. from.: the. system` for." separate l processingV to; recover oxygenated compoundsi,` for. example;

processing by solvent extraction. or lay-treatment.

with ari-adsorbent., ifdesired'but these ad.'ditional.Y

processing treatments;` are, not i intended; to` be parts of this` invention, @then accessories areconventional types ofeduipmentwhich` may be.-

employed, even though omittediromthe drawing for the sake of simplicity.

The non-polar.:` solventJ ernplmiedras;` internat.

reiiux in the second fractional,` distillation zone may be a hydrocarbon which remains liquid under conditions existing inthefractionation Zone. Suitable-hydrocarbon liquids for use. in the'process-include reflned'white oils', pure paraiiins, oleiins, naphthenes; aromaticsand mixtures thereof.4 Fractions from virgin or cracked hydrocarbon stocks may beused.` The initial boiling point ofthe hydrocarbonshould preferably notbe appreciably lower than that of thehighest boiling oxygenated component to be separated. 'Ihe final boiling point of; the hydrocarbon is not materialy except that the hydrocarbon must be i line fractions-including gasoline fractions rrecov'- i eredfrom. the product of the catalytic hydrogenation of carbon monoxide may also be' employed. Some of the gasoline fractions may contain light endswhich boil below about 175 F. are perfectly operable as solvents but are not preferred due to the` possibility 0fv azeotrope formationbetween:` the lower boiling hydrocarbons in the fraction with the oxygenated.` compounds present. If. the light ends are present only in small, amounts their presence can be tolerated.

A basic advantage of the process described is that it enablesone to obtain the desired alcohols (bottoms from the rst Water extractive distillation zone, andl overhead from the second nonpolar solvent extractive distillation zone)` With.- out having to isolate any o1 the other oxygenated impurities. In addition the otherimpurties are obtained in anhydrous` form sothat they` may It is preferredV to use a` hydro-H be; processed for. orwincorporated directlyy into gasoline as .blending agents.`

This unitary. process particularly. suited. to.

the Workup of mixtures. ofl oxygenated compoundsnincluding two l or` more alcohols obtained from the.` catalytichydrogenaton ofrcarbon mon-ii oxide, when the second.: alcohol` comprises:` lessthan 25%. ofwthematerialfprocessedi in thelsecf` ond` extractiva` distillation tower;`

Basic data havebeenobtained. in theapplicationiof the process as..describedzin.Example Igbe-` lovvifortheirecovery. offpuried'ethanol and puri'.- iied isopropanolas two main. separate products inthe treatmentof; aqueous. crude mixtures of these alcoholsicontained; in i a .mixture with. other.'

oxygenated` confiponents:` listed in Example I:

'Ihese-` data` clearly demonstrate that Withysufi-L ciently large concentrations of Water in the inter-r.

nal reux ovving down. througha fractional distillationzone, the isopropyl,alcoholandany attendant non-alcoholic neutral4 oxygenated com pounds are rendered. much.. more. volatile than the` ethyl. alcoholsoI that. the. ethyl. alcohol re-i mains isolated intheaqueous reflux. These data,

also indicate that alarge. proportionA oi `Water vapor tends to be present with the vaporizedisopropanol that leaves the upper part of a rectifying section in which the ethanol vaporization is sunlciently depressed to eitect the separation of the ethanol from the isopropanol. With the vaporized isopropanol leaving the upper part of the rectifying section there are present other neutral organic compounds which contaminated the ethyl alcohols in the initial feed since these contaminants are even more readily volatilized than. the isopropanol.

Similar-application of the process can be made to eiectthe separation of n-propanol from a mixture containing higher alcohols among other constituents as described in Example II below.

EXAMPLE I .An aqueous mixture containing ethanol, isopropanol and non-alcoholic neutral oxygenated compounds such as acetone, methyl ethyl ketone, n-butyraldehyde, n-valeraldehyde, ethyl acetate and'n-ipropyl acetate was fed to a rst extraotive distillation column where the mixture Was distilledv andthe vapors rose-` through the column. countercurrentl to an internal liquid aqueousA reflux-.containing approximately moli percent Water: components. present: boil inr the Wet stata up to 82A? 61;. Ethyl alcohol; dissolved; inwater; was` remorediasrbottoms ircmf the-.-rstcolumn,y While l isopropanol;` andV the4 oxygenated compounds dis.

tilledoverheadtogether with, some l ofV the Water. The overhead was condensed andledtoia second extractiva` distillation column wherein the. va.-

pors were distilled countercurrent to. an internal,

liquid redux: containing approximately 9|llv0lume percentd of a highly refined parafiinic t. oil boilingcompounds were` removed from thefbottom. of. .the columntin substantially anhydrous condition .dis, solved in]` the oils-solvent.

EXAMPLE. 1I

The` process;V as set; forth. in` Example I Was` re-` peated With a. synthetic aqueous feed` stock. con;-` tainingy n--propanoh` n-butanolL secondary and.

iso-butanoL. pentanolfz. methyl propyl ketone.

methyl, isobut'yl ketone. f isoxaleraldebydagand. Ils-- The non -alcoholic'- neutral` oxygenated` v butyl acetate. An aqueous reux containing approximately 95 mol per cent Water was employed. The non-alcoholic neutral oxygenated compounds present boiled in the Wet state at temperatures up to 90.2 C. Normal propanol dissolved in Water was recovered as bottoms from the first column, While the remaining alcohols and nonalcohol neutral oxygenated components distilled overhead substantially free of n-propanol. When the overhead from the rst column was extractively distilled employing the same concentration of the same oil solvent as used in Example I the remaining alcohols, viz., the butanols and pentanol-2 together with the Water were recovered as vapors in the overhead, While the ketones, isovaleraldehyde and n-butyl acetate in substantially anhydrous condition Were removed as bottoms.

EXAMPLE III A hydrocarbon synthesis product containing aqueous Cz-Cs alcohols together with non-alcoholic neutral oxygenated compounds such as aldehydes, ketones and esters boiling in the same range Was distilled in an extractive distillation mately 4.3 volume percent of alcohols chieiiy C3- Cs alcohols. The lower aqueous phase was Withdrawn at a rate of 22 cc./hr. It contained 75 volume percent alcohols chiefly Ca-Cs alcohols. A total of 34 volume percent of the alcohols in the feed Were taken overhead. The balance of the alcohols were recovered With the neutral non-alooholic oxygenated compounds as a solution in the gasoline as bottoms from the column. A'

much cleaner split could have been made by taking more overhead from the column.

The volatilities of eighteen different oxygenated compounds relative to ethanol as a function of Water concentration are presented in Table I. The data contained therein will enable one to chose the proper Water concentration required for any given separation indicated.

The relative volatilities of seven different systems in a non-polar solvent, specifically a highly refined paraiinic White oil are set forth in Table II. The data show that in the presence of the White oil solvent at the concentration given the alcohols are more volatile than the non-alcoholic neutral compounds, and the alphas are suicolumn employing Water in concentrations of cently high to eiTect the separation.

TABLE I Volatilities relative to ethanol' as a; function of water concentration Oxygenated Compound Mol Percent Water n-Pcntanol iso-Propanol iso-Butanol. sec-ButanoL Pentanol-2.. Propionaldehyde n-Valeraldehyde.

Acetone 2. 95

i-Valeraldehyde Methyl propyl Ketone Ethyl Acetate.

n-Propyl Acetate approximately 90 mol percent in the internal liquid reux. The feed contained approximately 79 weight percent alcohols; 0.1 weight percent C3 aldehydes; 0.6 weight percent C3 ketones; 0.3 weight percent C3 esters; 0.9 Weight percent acetals; 0.2 Weight percent C2 acids; and the balance water. Substantially all the ethanol was removed from the mixture as an aqueous solution as bottoms from the column. The small amount of acids present were recovered in the bottoms With the ethanol. The overhead was condensed and fed to a second extractive distlllation column employing an internal liquid reux containing approximately 90 vol. percent of a gasoline obtained from the catalytic hydrogenation of carbon monoxide. The gasoline had an initial boiling point of 131 F. and a final boiling point of 419 F. The bulk of the gasoline boiled between 187 F. and 390 F. The overhead from the first column Was fed to the second column at a rate of 64 cc./hr., While the gasoline solvent was fed at the rate of 600 cc./hr. The distillate separated into tWo phases. Of the hydrocarbon phase 78 cc./hr. was refluxed to the column through the solvent preheater while the balance of 26 cc./hr. was withdrawn from the system. The hydrocarbon phase contained approxi- 1 Highly refined parailnic fraction B. P. 396-522" F., sp. gr. 0.800, aniline pt. 176 F., flush 160 F., viscosity at 100 F.-30 SS U.

What is claimed is:

l. The method of separating and recovering npropanol n-butanol and close-boiling non-alcoholic saturated unsubstituted neutral oxygenated compounds from mixtures thereof which comprises, introducing the mixture into a rst fractionation zone wherein vapors of the alcohols and oxygenated compounds ascend counter-currently to a liquid reflux of said vapors dissolved in to 99 mol percent of Water to effect a higher vaporization of the n-butanol and of the oxygen-l ated compounds than of n-propanol, removing a solution of n-propanol in water from a bottom portion of the first fractionation zone, withdrawing n-butanol, the oxygenated compounds and Water as overhead from the rst fractionation zone, introducing the n-butanol, oxygenated compounds and water into a second fractionation zone wherein vapors of the n-butanol, oxygenfated compounds and Water ascend countercurrently to a liquid reux of said vapors dissolved in 70 to 99 volume percent of a liquid hydrocarbon solvent which does not azeotropically distill to any appreciable extent from the second fractionation zone to effect a higher vaporization of the n-butanol and Water than of the oxygenated compounds, recovering n-butanol and water as overhead from the second fractionation zone, and recovering a solution of the oxygenated compounds and hydrocarbon solvent in substantially anhydrous condition from ya bottom portion of the second fractionation zone.

2. The method according to claim 1 in which the oxygenated compound present boil in the wet state at temperatures up to 90.2 C.

3. The method according to claim 1 in which the mixture also contains other C4. and Cs aliphatic alcohols which are recovered overhead from the second fractionation zone together with the n-butanol, and in which the hydrocarbon solvent is a highly refined parafnic oil boiling in the range of 396 F. to 522 F.

CARL S. CARLSON.

PAUL V. SMITH, JR.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 887,793 Guillaume May 19, 1908 996,328 Guillaume June 27, 1911 1,929,901 Ricard et a1. Oct. 10, 1933 2,107,265 Archibald Feb. 8, 1938 2,148,846 Von Retze et al Feb. 28, 1939 2,198,651 Bludworth Apr. 30, 1940 2,290,442 Metal July 21, 1942 2,290,636 Deanesly July 21, 1942 2,351,527 Lembecke June 13, 1944 2,386,058 Patterson et al Oct. 2, 1945 2,434,424 Morris et al Jan. 13, 1948 2,476,205 McCants July 12, 1949 2,476,206 McCants July 12, 1949 2,477,087 Robertson July 26, 1949 2,483,246 Stribley Sept. 27, 1949 2,500,596 Adelson Mar. 14, 1950 2,551,593 Gilliland et al May 8, 1951 2,591,712 Morrell et al. Apr. 8, 1952 2,591,713 Morrell et al Apr. 8, 1952 

1. THE METHOD OF SEPARATING AND RECOVERING NPROPANOL N-BUTANOL AND CLOSE-BOILING NON-ALCOHOLIC SATURATED UNSUBSTITUTED NEUTRAL OXYGENATED COMPOUNDS FROM MIXTURES THEREOF WHICH COMPRISES, INTRODUCING THE MIXTURE INTO A FIRST FRACTIONATION ZONE WHEREIN VAPORS OF THE ALCOHOLS AND OXYGENATED COMPOUNDS ASCEND COUNTER-CURRENTLY TO A LIQUID REFLUX OF SAID VAPORS DISSOLVED IN 95 TO 99 MOL PERCENT OF WATER TO EFFECT A HIGHER VAPORIZATION OF THE N-BUTANOL AND OF THE OXYGENATED COMPOUNDS THAN OF N-PROPANOL, REMOVING A SOLUTION OF N-PROPANOL IN WATER FROM A BOTTOM PORTION OF THE FIRST FRACTIONATION ZONE, WITHDRAWING N-BUTANOL, THE OXYGENATED COMPOUNDS AND WATER AS OVERHEAD FROM THE FIRST FRACTIONATION ZONE, INTRODUCING THE N-BUTANOL, OXYGENATED COMPOUNDS AND WATER INTO A SECOND FRACTIONATION ZONE WHEREIN VAPORS OF THE N-BUTANOL, OXYGENATED COMPOUNDS AND WATER ASCEND COUNTERCURRENTLY TO A LIQUID REFLUX OF SAID VAPORS DISSOLVED IN 70 TO 99 VOLUME PERCENT OF A LIQUID HYDROCARBON SOLVENT WHICH DOES NOT AZEOTROPICALLY DISTILL TO ANY APPRECIABLE EXTENT FROM THE SECOND FRACTIONATION ZONE TO EFFECT A HIGHER VAPORIZATION OF THE N-BUTANOL AND WATER THAN OF THE OXYGENATED COMPOUNDS, RECOVERING N-BUTANOL AND WATER AS OVERHEAD FROM THE SECOND FRACTIONATION ZONE, AND RECOVERING A SOLUTION OF THE OXYGENATED COMPOUNDS AND HYDROCARBON SOLVENT IN SUBSTANTIALLY ANHYDROUS CONDITION FROM A BOTTOM PORTION OF THE SECOND FRACTIONATION ZONE. 